I have a 20 gallon long tank with a cage topper on it. The cage portion has some boards for their comfort. I actually have two gerbils, they're brothers. The one that is sick has sat on the boards for several hours and not produced any pellets. I also haven't seen any evidence of urine from him.
I am leaning toward him being constipated because he still took a sunflower seed from me when I offered it to him, and he was at the water bottle earlier. He is not underweight, he is actually a bit overweight.
I use carefresh bedding and do not use any fiber nest materials as I had already been warned that they could cause problems with blockage as well as wrapping around their limbs and causing harm.
His usual diet consists of the commercial gerbil mix you can get at Walmart, Petsmart or Petco with the mix of seeds and what look to be cereal pieces. He also gets seeds - sunflower, pumpkin, watermelon, etc (it is a bag also purchased at Petsmart called Extreme select seeds by Browns). I also have a mix of raisins, papaya and rose hips. Fresh hay at least once a week, a pressed hay cube is in there, and pressed cubes of mouse/gerbil/hamster food. I gave him a piece of broccoli two days ago and he ate some of it.
If anything, I am guilty of giving too many treats, I think. I occasionally give them mealworms, which they enjoy, but haven't done so in several weeks.
Oddly enough, it was because of a mix up in gender when my girlfriend bought her gerbils that I even have any. Her pair gave birth to a relatively small litter (3 total) and they were all males. Her husband checked multiple times to make absolutely sure that the two I got were both males.
The other reason I don't think this is a case of pregnancy is that he's not moving very much. He's hunched up and moves reluctantly even when I touch him (they're not used to being picked up). Also, if this were a case of pregnancy, I would expect to see nesting behavior, in which case the gerbil would either be in the house on the second level, or down in the tank where the bulk of the bedding is, creating a nest area for the babies.
Both gerbils will be a year old at the end of May. They've never been exposed to pet store conditions - I got them from my girlfriend when they were 8 weeks old and weaned.
Since there is an absence of pellets, and he's hunched up as if his tummy hurts, I'm thinking it's either constipation or some sort of blockage, though I don't know what may have caused a blockage.
What remedies can I try for constipation?